The invention relates to a semiconductor detector for radiation detection and also to an associated operating method.
From Gerhard Lutz: “Semiconductor Radiation Detectors”, 2nd edition 2001, Springer-Verlag, pages 144-152, pnCCD detectors are known in which the incident radiation in a pnCCD structure generates signal electrons which are transported along the pnCCD structure to a readout anode. Such pnCCD detectors on highly resistive n-doped silicon have reached a level of maturity close to their physical limits. For example, the noise of the best pnCCD detectors is just 1.5 electrons at a power consumption of approx. 0.3 mW per channel.
This good noise behavior can be achieved in the conventional pnCCD detectors by a capacitance-free clearing mechanism which is described for example in Carlo Fiorini, Peter Lechner: “Continuous Charge Restoration in Semiconductor Detectors by Means of the Gate-to-Drain Current of the Integrated Front-End JFET”, IEEE Transactions on Nuclear Science, Vol. 46, No. 3, June 1999, pages 761-764. With this clearing mechanism, the readout anode of the pnCCD detector is reset to its original potential through a so-called “Weak Avalanche” process by means of a JFET transistor (JFET: Junction Field Effect Transistor). However, this conventional clearing mechanism is unsuitable for clearing large signal charge quantities. Furthermore, this conventional clearing mechanism does not allow rapid clearing of the signal charges in the nanosecond range.
Another clearing mechanism for a pnCCD detector is known from Pinotti, E. et al.: “The pn-CCD on-chip electronics”, Nuclear Instruments and Methods in Physics Research A326 (1993) 85-91, in which the signal charge carriers are removed from the readout anode of the pnCCD detector by an integrated field effect transistor. However, this clearing mechanism has a disadvantageous effect on the capacitance of the readout anode.
The object of the invention is therefore to create a semiconductor detector with an improved clearing mechanism and to provide a correspondingly improved operating method for such a semiconductor detector. Here, the clearing mechanism according to the invention should preferably be capacitance-free and should allow rapid clearing of large signal charge quantities in the nanosecond range.
This object is achieved by a semiconductor detector according to the invention and by a corresponding operating method.